6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2024-09-07 01:54:50 +00:00
Code Issues Projects Releases Wiki Activity
6bb0bd52ec
llvm-6502/lib/Transforms/Scalar/GVN.cpp
Owen Anderson 6bb0bd52ec Improve the return slot optimization to be both more aggressive (not limited to sret parameters), and 
safer (when the passed pointer might be invalid).  Thanks to Duncan and Chris for the idea behind this, 
and extra thanks to Duncan for helping me work out the trap-safety.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48280 91177308-0d34-0410-b5e6-96231b3b80d8
2008-03-12 07:37:44 +00:00

1393 lines
44 KiB
C++
Raw Blame History

//===- GVN.cpp - Eliminate redundant values and loads ------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs global value numbering to eliminate fully redundant
// instructions. It also performs simple dead load elimination.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "gvn"
#include "llvm/Transforms/Scalar.h"
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Instructions.h"
#include "llvm/ParameterAttributes.h"
#include "llvm/Value.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Target/TargetData.h"
using namespace llvm;
//===----------------------------------------------------------------------===//
// ValueTable Class
//===----------------------------------------------------------------------===//
/// This class holds the mapping between values and value numbers. It is used
/// as an efficient mechanism to determine the expression-wise equivalence of
/// two values.
namespace {
struct VISIBILITY_HIDDEN Expression {
enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, EMPTY,
TOMBSTONE };
ExpressionOpcode opcode;
const Type* type;
uint32_t firstVN;
uint32_t secondVN;
uint32_t thirdVN;
SmallVector<uint32_t, 4> varargs;
Value* function;
Expression() { }
Expression(ExpressionOpcode o) : opcode(o) { }
bool operator==(const Expression &other) const {
if (opcode != other.opcode)
return false;
else if (opcode == EMPTY || opcode == TOMBSTONE)
return true;
else if (type != other.type)
return false;
else if (function != other.function)
return false;
else if (firstVN != other.firstVN)
return false;
else if (secondVN != other.secondVN)
return false;
else if (thirdVN != other.thirdVN)
return false;
else {
if (varargs.size() != other.varargs.size())
return false;
for (size_t i = 0; i < varargs.size(); ++i)
if (varargs[i] != other.varargs[i])
return false;
return true;
}
}
bool operator!=(const Expression &other) const {
if (opcode != other.opcode)
return true;
else if (opcode == EMPTY || opcode == TOMBSTONE)
return false;
else if (type != other.type)
return true;
else if (function != other.function)
return true;
else if (firstVN != other.firstVN)
return true;
else if (secondVN != other.secondVN)
return true;
else if (thirdVN != other.thirdVN)
return true;
else {
if (varargs.size() != other.varargs.size())
return true;
for (size_t i = 0; i < varargs.size(); ++i)
if (varargs[i] != other.varargs[i])
return true;
return false;
}
}
};
class VISIBILITY_HIDDEN ValueTable {
private:
DenseMap<Value*, uint32_t> valueNumbering;
DenseMap<Expression, uint32_t> expressionNumbering;
AliasAnalysis* AA;
uint32_t nextValueNumber;
Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
Expression::ExpressionOpcode getOpcode(CmpInst* C);
Expression::ExpressionOpcode getOpcode(CastInst* C);
Expression create_expression(BinaryOperator* BO);
Expression create_expression(CmpInst* C);
Expression create_expression(ShuffleVectorInst* V);
Expression create_expression(ExtractElementInst* C);
Expression create_expression(InsertElementInst* V);
Expression create_expression(SelectInst* V);
Expression create_expression(CastInst* C);
Expression create_expression(GetElementPtrInst* G);
Expression create_expression(CallInst* C);
public:
ValueTable() : nextValueNumber(1) { }
uint32_t lookup_or_add(Value* V);
uint32_t lookup(Value* V) const;
void add(Value* V, uint32_t num);
void clear();
void erase(Value* v);
unsigned size();
void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
uint32_t hash_operand(Value* v);
};
}
namespace llvm {
template <> struct DenseMapInfo<Expression> {
static inline Expression getEmptyKey() {
return Expression(Expression::EMPTY);
}
static inline Expression getTombstoneKey() {
return Expression(Expression::TOMBSTONE);
}
static unsigned getHashValue(const Expression e) {
unsigned hash = e.opcode;
hash = e.firstVN + hash * 37;
hash = e.secondVN + hash * 37;
hash = e.thirdVN + hash * 37;
hash = ((unsigned)((uintptr_t)e.type >> 4) ^
(unsigned)((uintptr_t)e.type >> 9)) +
hash * 37;
for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
E = e.varargs.end(); I != E; ++I)
hash = *I + hash * 37;
hash = ((unsigned)((uintptr_t)e.function >> 4) ^
(unsigned)((uintptr_t)e.function >> 9)) +
hash * 37;
return hash;
}
static bool isEqual(const Expression &LHS, const Expression &RHS) {
return LHS == RHS;
}
static bool isPod() { return true; }
};
}
//===----------------------------------------------------------------------===//
// ValueTable Internal Functions
//===----------------------------------------------------------------------===//
Expression::ExpressionOpcode
ValueTable::getOpcode(BinaryOperator* BO) {
switch(BO->getOpcode()) {
case Instruction::Add:
return Expression::ADD;
case Instruction::Sub:
return Expression::SUB;
case Instruction::Mul:
return Expression::MUL;
case Instruction::UDiv:
return Expression::UDIV;
case Instruction::SDiv:
return Expression::SDIV;
case Instruction::FDiv:
return Expression::FDIV;
case Instruction::URem:
return Expression::UREM;
case Instruction::SRem:
return Expression::SREM;
case Instruction::FRem:
return Expression::FREM;
case Instruction::Shl:
return Expression::SHL;
case Instruction::LShr:
return Expression::LSHR;
case Instruction::AShr:
return Expression::ASHR;
case Instruction::And:
return Expression::AND;
case Instruction::Or:
return Expression::OR;
case Instruction::Xor:
return Expression::XOR;
// THIS SHOULD NEVER HAPPEN
default:
assert(0 && "Binary operator with unknown opcode?");
return Expression::ADD;
}
}
Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
if (C->getOpcode() == Instruction::ICmp) {
switch (C->getPredicate()) {
case ICmpInst::ICMP_EQ:
return Expression::ICMPEQ;
case ICmpInst::ICMP_NE:
return Expression::ICMPNE;
case ICmpInst::ICMP_UGT:
return Expression::ICMPUGT;
case ICmpInst::ICMP_UGE:
return Expression::ICMPUGE;
case ICmpInst::ICMP_ULT:
return Expression::ICMPULT;
case ICmpInst::ICMP_ULE:
return Expression::ICMPULE;
case ICmpInst::ICMP_SGT:
return Expression::ICMPSGT;
case ICmpInst::ICMP_SGE:
return Expression::ICMPSGE;
case ICmpInst::ICMP_SLT:
return Expression::ICMPSLT;
case ICmpInst::ICMP_SLE:
return Expression::ICMPSLE;
// THIS SHOULD NEVER HAPPEN
default:
assert(0 && "Comparison with unknown predicate?");
return Expression::ICMPEQ;
}
} else {
switch (C->getPredicate()) {
case FCmpInst::FCMP_OEQ:
return Expression::FCMPOEQ;
case FCmpInst::FCMP_OGT:
return Expression::FCMPOGT;
case FCmpInst::FCMP_OGE:
return Expression::FCMPOGE;
case FCmpInst::FCMP_OLT:
return Expression::FCMPOLT;
case FCmpInst::FCMP_OLE:
return Expression::FCMPOLE;
case FCmpInst::FCMP_ONE:
return Expression::FCMPONE;
case FCmpInst::FCMP_ORD:
return Expression::FCMPORD;
case FCmpInst::FCMP_UNO:
return Expression::FCMPUNO;
case FCmpInst::FCMP_UEQ:
return Expression::FCMPUEQ;
case FCmpInst::FCMP_UGT:
return Expression::FCMPUGT;
case FCmpInst::FCMP_UGE:
return Expression::FCMPUGE;
case FCmpInst::FCMP_ULT:
return Expression::FCMPULT;
case FCmpInst::FCMP_ULE:
return Expression::FCMPULE;
case FCmpInst::FCMP_UNE:
return Expression::FCMPUNE;
// THIS SHOULD NEVER HAPPEN
default:
assert(0 && "Comparison with unknown predicate?");
return Expression::FCMPOEQ;
}
}
}
Expression::ExpressionOpcode
ValueTable::getOpcode(CastInst* C) {
switch(C->getOpcode()) {
case Instruction::Trunc:
return Expression::TRUNC;
case Instruction::ZExt:
return Expression::ZEXT;
case Instruction::SExt:
return Expression::SEXT;
case Instruction::FPToUI:
return Expression::FPTOUI;
case Instruction::FPToSI:
return Expression::FPTOSI;
case Instruction::UIToFP:
return Expression::UITOFP;
case Instruction::SIToFP:
return Expression::SITOFP;
case Instruction::FPTrunc:
return Expression::FPTRUNC;
case Instruction::FPExt:
return Expression::FPEXT;
case Instruction::PtrToInt:
return Expression::PTRTOINT;
case Instruction::IntToPtr:
return Expression::INTTOPTR;
case Instruction::BitCast:
return Expression::BITCAST;
// THIS SHOULD NEVER HAPPEN
default:
assert(0 && "Cast operator with unknown opcode?");
return Expression::BITCAST;
}
}
uint32_t ValueTable::hash_operand(Value* v) {
if (CallInst* CI = dyn_cast<CallInst>(v))
if (!AA->doesNotAccessMemory(CI))
return nextValueNumber++;
return lookup_or_add(v);
}
Expression ValueTable::create_expression(CallInst* C) {
Expression e;
e.type = C->getType();
e.firstVN = 0;
e.secondVN = 0;
e.thirdVN = 0;
e.function = C->getCalledFunction();
e.opcode = Expression::CALL;
for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
I != E; ++I)
e.varargs.push_back(hash_operand(*I));
return e;
}
Expression ValueTable::create_expression(BinaryOperator* BO) {
Expression e;
e.firstVN = hash_operand(BO->getOperand(0));
e.secondVN = hash_operand(BO->getOperand(1));
e.thirdVN = 0;
e.function = 0;
e.type = BO->getType();
e.opcode = getOpcode(BO);
return e;
}
Expression ValueTable::create_expression(CmpInst* C) {
Expression e;
e.firstVN = hash_operand(C->getOperand(0));
e.secondVN = hash_operand(C->getOperand(1));
e.thirdVN = 0;
e.function = 0;
e.type = C->getType();
e.opcode = getOpcode(C);
return e;
}
Expression ValueTable::create_expression(CastInst* C) {
Expression e;
e.firstVN = hash_operand(C->getOperand(0));
e.secondVN = 0;
e.thirdVN = 0;
e.function = 0;
e.type = C->getType();
e.opcode = getOpcode(C);
return e;
}
Expression ValueTable::create_expression(ShuffleVectorInst* S) {
Expression e;
e.firstVN = hash_operand(S->getOperand(0));
e.secondVN = hash_operand(S->getOperand(1));
e.thirdVN = hash_operand(S->getOperand(2));
e.function = 0;
e.type = S->getType();
e.opcode = Expression::SHUFFLE;
return e;
}
Expression ValueTable::create_expression(ExtractElementInst* E) {
Expression e;
e.firstVN = hash_operand(E->getOperand(0));
e.secondVN = hash_operand(E->getOperand(1));
e.thirdVN = 0;
e.function = 0;
e.type = E->getType();
e.opcode = Expression::EXTRACT;
return e;
}
Expression ValueTable::create_expression(InsertElementInst* I) {
Expression e;
e.firstVN = hash_operand(I->getOperand(0));
e.secondVN = hash_operand(I->getOperand(1));
e.thirdVN = hash_operand(I->getOperand(2));
e.function = 0;
e.type = I->getType();
e.opcode = Expression::INSERT;
return e;
}
Expression ValueTable::create_expression(SelectInst* I) {
Expression e;
e.firstVN = hash_operand(I->getCondition());
e.secondVN = hash_operand(I->getTrueValue());
e.thirdVN = hash_operand(I->getFalseValue());
e.function = 0;
e.type = I->getType();
e.opcode = Expression::SELECT;
return e;
}
Expression ValueTable::create_expression(GetElementPtrInst* G) {
Expression e;
e.firstVN = hash_operand(G->getPointerOperand());
e.secondVN = 0;
e.thirdVN = 0;
e.function = 0;
e.type = G->getType();
e.opcode = Expression::GEP;
for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
I != E; ++I)
e.varargs.push_back(hash_operand(*I));
return e;
}
//===----------------------------------------------------------------------===//
// ValueTable External Functions
//===----------------------------------------------------------------------===//
/// lookup_or_add - Returns the value number for the specified value, assigning
/// it a new number if it did not have one before.
uint32_t ValueTable::lookup_or_add(Value* V) {
DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
if (VI != valueNumbering.end())
return VI->second;
if (CallInst* C = dyn_cast<CallInst>(V)) {
if (AA->onlyReadsMemory(C)) { // includes doesNotAccessMemory
Expression e = create_expression(C);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
Expression e = create_expression(BO);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
Expression e = create_expression(C);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (CastInst* U = dyn_cast<CastInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
}
/// lookup - Returns the value number of the specified value. Fails if
/// the value has not yet been numbered.
uint32_t ValueTable::lookup(Value* V) const {
DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
if (VI != valueNumbering.end())
return VI->second;
else
assert(0 && "Value not numbered?");
return 0;
}
/// clear - Remove all entries from the ValueTable
void ValueTable::clear() {
valueNumbering.clear();
expressionNumbering.clear();
nextValueNumber = 1;
}
/// erase - Remove a value from the value numbering
void ValueTable::erase(Value* V) {
valueNumbering.erase(V);
}
//===----------------------------------------------------------------------===//
// ValueNumberedSet Class
//===----------------------------------------------------------------------===//
namespace {
class ValueNumberedSet {
private:
SmallPtrSet<Value*, 8> contents;
BitVector numbers;
public:
ValueNumberedSet() { numbers.resize(1); }
ValueNumberedSet(const ValueNumberedSet& other) {
numbers = other.numbers;
contents = other.contents;
}
typedef SmallPtrSet<Value*, 8>::iterator iterator;
iterator begin() { return contents.begin(); }
iterator end() { return contents.end(); }
bool insert(Value* v) { return contents.insert(v); }
void insert(iterator I, iterator E) { contents.insert(I, E); }
void erase(Value* v) { contents.erase(v); }
unsigned count(Value* v) { return contents.count(v); }
size_t size() { return contents.size(); }
void set(unsigned i) {
if (i >= numbers.size())
numbers.resize(i+1);
numbers.set(i);
}
void operator=(const ValueNumberedSet& other) {
contents = other.contents;
numbers = other.numbers;
}
void reset(unsigned i) {
if (i < numbers.size())
numbers.reset(i);
}
bool test(unsigned i) {
if (i >= numbers.size())
return false;
return numbers.test(i);
}
void clear() {
contents.clear();
numbers.clear();
}
};
}
//===----------------------------------------------------------------------===//
// GVN Pass
//===----------------------------------------------------------------------===//
namespace {
class VISIBILITY_HIDDEN GVN : public FunctionPass {
bool runOnFunction(Function &F);
public:
static char ID; // Pass identification, replacement for typeid
GVN() : FunctionPass((intptr_t)&ID) { }
private:
ValueTable VN;
DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
PhiMapType phiMap;
// This transformation requires dominator postdominator info
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<DominatorTree>();
AU.addRequired<MemoryDependenceAnalysis>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<TargetData>();
AU.addPreserved<AliasAnalysis>();
AU.addPreserved<MemoryDependenceAnalysis>();
AU.addPreserved<TargetData>();
}
// Helper fuctions
// FIXME: eliminate or document these better
Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
void val_insert(ValueNumberedSet& s, Value* v);
bool processLoad(LoadInst* L,
DenseMap<Value*, LoadInst*>& lastLoad,
SmallVector<Instruction*, 4>& toErase);
bool processInstruction(Instruction* I,
ValueNumberedSet& currAvail,
DenseMap<Value*, LoadInst*>& lastSeenLoad,
SmallVector<Instruction*, 4>& toErase);
bool processNonLocalLoad(LoadInst* L,
SmallVector<Instruction*, 4>& toErase);
bool processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
SmallVector<Instruction*, 4>& toErase);
bool performCallSlotOptzn(MemCpyInst* cpy, CallInst* C,
SmallVector<Instruction*, 4>& toErase);
Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
DenseMap<BasicBlock*, Value*> &Phis,
bool top_level = false);
void dump(DenseMap<BasicBlock*, Value*>& d);
bool iterateOnFunction(Function &F);
Value* CollapsePhi(PHINode* p);
bool isSafeReplacement(PHINode* p, Instruction* inst);
};
char GVN::ID = 0;
}
// createGVNPass - The public interface to this file...
FunctionPass *llvm::createGVNPass() { return new GVN(); }
static RegisterPass<GVN> X("gvn",
"Global Value Numbering");
STATISTIC(NumGVNInstr, "Number of instructions deleted");
STATISTIC(NumGVNLoad, "Number of loads deleted");
/// find_leader - Given a set and a value number, return the first
/// element of the set with that value number, or 0 if no such element
/// is present
Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
if (!vals.test(v))
return 0;
for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
I != E; ++I)
if (v == VN.lookup(*I))
return *I;
assert(0 && "No leader found, but present bit is set?");
return 0;
}
/// val_insert - Insert a value into a set only if there is not a value
/// with the same value number already in the set
void GVN::val_insert(ValueNumberedSet& s, Value* v) {
uint32_t num = VN.lookup(v);
if (!s.test(num))
s.insert(v);
}
void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
printf("{\n");
for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
E = d.end(); I != E; ++I) {
if (I->second == MemoryDependenceAnalysis::None)
printf("None\n");
else
I->second->dump();
}
printf("}\n");
}
Value* GVN::CollapsePhi(PHINode* p) {
DominatorTree &DT = getAnalysis<DominatorTree>();
Value* constVal = p->hasConstantValue();
if (constVal) {
if (Instruction* inst = dyn_cast<Instruction>(constVal)) {
if (DT.dominates(inst, p))
if (isSafeReplacement(p, inst))
return inst;
} else {
return constVal;
}
}
return 0;
}
bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
if (!isa<PHINode>(inst))
return true;
for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
UI != E; ++UI)
if (PHINode* use_phi = dyn_cast<PHINode>(UI))
if (use_phi->getParent() == inst->getParent())
return false;
return true;
}
/// GetValueForBlock - Get the value to use within the specified basic block.
/// available values are in Phis.
Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
DenseMap<BasicBlock*, Value*> &Phis,
bool top_level) {
// If we have already computed this value, return the previously computed val.
DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
if (V != Phis.end() && !top_level) return V->second;
BasicBlock* singlePred = BB->getSinglePredecessor();
if (singlePred) {
Value *ret = GetValueForBlock(singlePred, orig, Phis);
Phis[BB] = ret;
return ret;
}
// Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
// now, then get values to fill in the incoming values for the PHI.
PHINode *PN = new PHINode(orig->getType(), orig->getName()+".rle",
BB->begin());
PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
if (Phis.count(BB) == 0)
Phis.insert(std::make_pair(BB, PN));
// Fill in the incoming values for the block.
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
Value* val = GetValueForBlock(*PI, orig, Phis);
PN->addIncoming(val, *PI);
}
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
AA.copyValue(orig, PN);
// Attempt to collapse PHI nodes that are trivially redundant
Value* v = CollapsePhi(PN);
if (v) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
MD.removeInstruction(PN);
PN->replaceAllUsesWith(v);
for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
E = Phis.end(); I != E; ++I)
if (I->second == PN)
I->second = v;
PN->eraseFromParent();
Phis[BB] = v;
return v;
}
// Cache our phi construction results
phiMap[orig->getPointerOperand()].insert(PN);
return PN;
}
/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
/// non-local by performing PHI construction.
bool GVN::processNonLocalLoad(LoadInst* L,
SmallVector<Instruction*, 4>& toErase) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
// Find the non-local dependencies of the load
DenseMap<BasicBlock*, Value*> deps;
MD.getNonLocalDependency(L, deps);
DenseMap<BasicBlock*, Value*> repl;
// Filter out useless results (non-locals, etc)
for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
I != E; ++I)
if (I->second == MemoryDependenceAnalysis::None) {
return false;
} else if (I->second == MemoryDependenceAnalysis::NonLocal) {
continue;
} else if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
if (S->getPointerOperand() == L->getPointerOperand())
repl[I->first] = S->getOperand(0);
else
return false;
} else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
if (LD->getPointerOperand() == L->getPointerOperand())
repl[I->first] = LD;
else
return false;
} else {
return false;
}
// Use cached PHI construction information from previous runs
SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
I != E; ++I) {
if ((*I)->getParent() == L->getParent()) {
MD.removeInstruction(L);
L->replaceAllUsesWith(*I);
toErase.push_back(L);
NumGVNLoad++;
return true;
} else {
repl.insert(std::make_pair((*I)->getParent(), *I));
}
}
// Perform PHI construction
SmallPtrSet<BasicBlock*, 4> visited;
Value* v = GetValueForBlock(L->getParent(), L, repl, true);
MD.removeInstruction(L);
L->replaceAllUsesWith(v);
toErase.push_back(L);
NumGVNLoad++;
return true;
}
/// processLoad - Attempt to eliminate a load, first by eliminating it
/// locally, and then attempting non-local elimination if that fails.
bool GVN::processLoad(LoadInst* L,
DenseMap<Value*, LoadInst*>& lastLoad,
SmallVector<Instruction*, 4>& toErase) {
if (L->isVolatile()) {
lastLoad[L->getPointerOperand()] = L;
return false;
}
Value* pointer = L->getPointerOperand();
LoadInst*& last = lastLoad[pointer];
// ... to a pointer that has been loaded from before...
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
bool removedNonLocal = false;
Instruction* dep = MD.getDependency(L);
if (dep == MemoryDependenceAnalysis::NonLocal &&
L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
removedNonLocal = processNonLocalLoad(L, toErase);
if (!removedNonLocal)
last = L;
return removedNonLocal;
}
bool deletedLoad = false;
// Walk up the dependency chain until we either find
// a dependency we can use, or we can't walk any further
while (dep != MemoryDependenceAnalysis::None &&
dep != MemoryDependenceAnalysis::NonLocal &&
(isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
// ... that depends on a store ...
if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
if (S->getPointerOperand() == pointer) {
// Remove it!
MD.removeInstruction(L);
L->replaceAllUsesWith(S->getOperand(0));
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
}
// Whether we removed it or not, we can't
// go any further
break;
} else if (!last) {
// If we don't depend on a store, and we haven't
// been loaded before, bail.
break;
} else if (dep == last) {
// Remove it!
MD.removeInstruction(L);
L->replaceAllUsesWith(last);
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
break;
} else {
dep = MD.getDependency(L, dep);
}
}
if (dep != MemoryDependenceAnalysis::None &&
dep != MemoryDependenceAnalysis::NonLocal &&
isa<AllocationInst>(dep)) {
// Check that this load is actually from the
// allocation we found
Value* v = L->getOperand(0);
while (true) {
if (BitCastInst *BC = dyn_cast<BitCastInst>(v))
v = BC->getOperand(0);
else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v))
v = GEP->getOperand(0);
else
break;
}
if (v == dep) {
// If this load depends directly on an allocation, there isn't
// anything stored there; therefore, we can optimize this load
// to undef.
MD.removeInstruction(L);
L->replaceAllUsesWith(UndefValue::get(L->getType()));
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
}
}
if (!deletedLoad)
last = L;
return deletedLoad;
}
/// performCallSlotOptzn - takes a memcpy and a call that it depends on,
/// and checks for the possibility of a call slot optimization by having
/// the call write its result directly into the destination of the memcpy.
bool GVN::performCallSlotOptzn(MemCpyInst* cpy, CallInst* C,
SmallVector<Instruction*, 4>& toErase) {
// The general transformation to keep in mind is
//
// call @func(..., src, ...)
// memcpy(dest, src, ...)
//
// ->
//
// memcpy(dest, src, ...)
// call @func(..., dest, ...)
//
// Since moving the memcpy is technically awkward, we additionally check that
// src only holds uninitialized values at the moment of the call, meaning that
// the memcpy can be discarded rather than moved.
// Deliberately get the source and destination with bitcasts stripped away,
// because we'll need to do type comparisons based on the underlying type.
Value* cpyDest = cpy->getDest();
Value* cpySrc = cpy->getSource();
CallSite CS = CallSite::get(C);
// We need to be able to reason about the size of the memcpy, so we require
// that it be a constant.
ConstantInt* cpyLength = dyn_cast<ConstantInt>(cpy->getLength());
if (!cpyLength)
return false;
// Require that src be an alloca. This simplifies the reasoning considerably.
AllocaInst* srcAlloca = dyn_cast<AllocaInst>(cpySrc);
if (!srcAlloca)
return false;
// Check that all of src is copied to dest.
TargetData& TD = getAnalysis<TargetData>();
ConstantInt* srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
if (!srcArraySize)
return false;
uint64_t srcSize = TD.getABITypeSize(srcAlloca->getAllocatedType()) *
srcArraySize->getZExtValue();
if (cpyLength->getZExtValue() < srcSize)
return false;
// Check that accessing the first srcSize bytes of dest will not cause a
// trap. Otherwise the transform is invalid since it might cause a trap
// to occur earlier than it otherwise would.
if (AllocaInst* A = dyn_cast<AllocaInst>(cpyDest)) {
// The destination is an alloca. Check it is larger than srcSize.
ConstantInt* destArraySize = dyn_cast<ConstantInt>(A->getArraySize());
if (!destArraySize)
return false;
uint64_t destSize = TD.getABITypeSize(A->getAllocatedType()) *
destArraySize->getZExtValue();
if (destSize < srcSize)
return false;
} else if (Argument* A = dyn_cast<Argument>(cpyDest)) {
// If the destination is an sret parameter then only accesses that are
// outside of the returned struct type can trap.
if (!A->hasStructRetAttr())
return false;
const Type* StructTy = cast<PointerType>(A->getType())->getElementType();
uint64_t destSize = TD.getABITypeSize(StructTy);
if (destSize < srcSize)
return false;
} else {
return false;
}
// Check that src is not accessed except via the call and the memcpy. This
// guarantees that it holds only undefined values when passed in (so the final
// memcpy can be dropped), that it is not read or written between the call and
// the memcpy, and that writing beyond the end of it is undefined.
SmallVector<User*, 8> srcUseList(srcAlloca->use_begin(),
srcAlloca->use_end());
while (!srcUseList.empty()) {
User* UI = srcUseList.back();
srcUseList.pop_back();
if (isa<GetElementPtrInst>(UI) || isa<BitCastInst>(UI)) {
for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
I != E; ++I)
srcUseList.push_back(*I);
} else if (UI != C && UI != cpy) {
return false;
}
}
// Since we're changing the parameter to the callsite, we need to make sure
// that what would be the new parameter dominates the callsite.
DominatorTree& DT = getAnalysis<DominatorTree>();
if (Instruction* cpyDestInst = dyn_cast<Instruction>(cpyDest))
if (!DT.dominates(cpyDestInst, C))
return false;
// In addition to knowing that the call does not access src in some
// unexpected manner, for example via a global, which we deduce from
// the use analysis, we also need to know that it does not sneakily
// access dest. We rely on AA to figure this out for us.
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
if (AA.getModRefInfo(C, cpy->getRawDest(), srcSize) !=
AliasAnalysis::NoModRef)
return false;
// All the checks have passed, so do the transformation.
for (unsigned i = 0; i < CS.arg_size(); ++i)
if (CS.getArgument(i) == cpySrc)
CS.setArgument(i, cpyDest);
// Drop any cached information about the call, because we may have changed
// its dependence information by changing its parameter.
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
MD.dropInstruction(C);
// Remove the memcpy
MD.removeInstruction(cpy);
toErase.push_back(cpy);
return true;
}
/// processMemCpy - perform simplication of memcpy's. If we have memcpy A which
/// copies X to Y, and memcpy B which copies Y to Z, then we can rewrite B to be
/// a memcpy from X to Z (or potentially a memmove, depending on circumstances).
/// This allows later passes to remove the first memcpy altogether.
bool GVN::processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
SmallVector<Instruction*, 4>& toErase) {
// We can only transforms memcpy's where the dest of one is the source of the
// other
if (M->getSource() != MDep->getDest())
return false;
// Second, the length of the memcpy's must be the same, or the preceeding one
// must be larger than the following one.
ConstantInt* C1 = dyn_cast<ConstantInt>(MDep->getLength());
ConstantInt* C2 = dyn_cast<ConstantInt>(M->getLength());
if (!C1 || !C2)
return false;
uint64_t DepSize = C1->getValue().getZExtValue();
uint64_t CpySize = C2->getValue().getZExtValue();
if (DepSize < CpySize)
return false;
// Finally, we have to make sure that the dest of the second does not
// alias the source of the first
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) !=
AliasAnalysis::NoAlias)
return false;
else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) !=
AliasAnalysis::NoAlias)
return false;
else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize)
!= AliasAnalysis::NoAlias)
return false;
// If all checks passed, then we can transform these memcpy's
Function* MemCpyFun = Intrinsic::getDeclaration(
M->getParent()->getParent()->getParent(),
M->getIntrinsicID());
std::vector<Value*> args;
args.push_back(M->getRawDest());
args.push_back(MDep->getRawSource());
args.push_back(M->getLength());
args.push_back(M->getAlignment());
CallInst* C = new CallInst(MemCpyFun, args.begin(), args.end(), "", M);
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
if (MD.getDependency(C) == MDep) {
MD.dropInstruction(M);
toErase.push_back(M);
return true;
} else {
MD.removeInstruction(C);
toErase.push_back(C);
return false;
}
}
/// processInstruction - When calculating availability, handle an instruction
/// by inserting it into the appropriate sets
bool GVN::processInstruction(Instruction* I,
ValueNumberedSet& currAvail,
DenseMap<Value*, LoadInst*>& lastSeenLoad,
SmallVector<Instruction*, 4>& toErase) {
if (LoadInst* L = dyn_cast<LoadInst>(I)) {
return processLoad(L, lastSeenLoad, toErase);
} else if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
// The are two possible optimizations we can do for memcpy:
// a) memcpy-memcpy xform which exposes redundance for DSE
// b) call-memcpy xform for return slot optimization
Instruction* dep = MD.getDependency(M);
if (dep == MemoryDependenceAnalysis::None ||
dep == MemoryDependenceAnalysis::NonLocal)
return false;
if (MemCpyInst *MemCpy = dyn_cast<MemCpyInst>(dep))
return processMemCpy(M, MemCpy, toErase);
if (CallInst* C = dyn_cast<CallInst>(dep))
return performCallSlotOptzn(M, C, toErase);
return false;
}
unsigned num = VN.lookup_or_add(I);
// Collapse PHI nodes
if (PHINode* p = dyn_cast<PHINode>(I)) {
Value* constVal = CollapsePhi(p);
if (constVal) {
for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
PI != PE; ++PI)
if (PI->second.count(p))
PI->second.erase(p);
p->replaceAllUsesWith(constVal);
toErase.push_back(p);
}
// Perform value-number based elimination
} else if (currAvail.test(num)) {
Value* repl = find_leader(currAvail, num);
if (CallInst* CI = dyn_cast<CallInst>(I)) {
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
if (!AA.doesNotAccessMemory(CI)) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
if (cast<Instruction>(repl)->getParent() != CI->getParent() ||
MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) {
// There must be an intervening may-alias store, so nothing from
// this point on will be able to be replaced with the preceding call
currAvail.erase(repl);
currAvail.insert(I);
return false;
}
}
}
// Remove it!
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
MD.removeInstruction(I);
VN.erase(I);
I->replaceAllUsesWith(repl);
toErase.push_back(I);
return true;
} else if (!I->isTerminator()) {
currAvail.set(num);
currAvail.insert(I);
}
return false;
}
// GVN::runOnFunction - This is the main transformation entry point for a
// function.
//
bool GVN::runOnFunction(Function& F) {
VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
bool changed = false;
bool shouldContinue = true;
while (shouldContinue) {
shouldContinue = iterateOnFunction(F);
changed |= shouldContinue;
}
return changed;
}
// GVN::iterateOnFunction - Executes one iteration of GVN
bool GVN::iterateOnFunction(Function &F) {
// Clean out global sets from any previous functions
VN.clear();
availableOut.clear();
phiMap.clear();
bool changed_function = false;
DominatorTree &DT = getAnalysis<DominatorTree>();
SmallVector<Instruction*, 4> toErase;
// Top-down walk of the dominator tree
for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
E = df_end(DT.getRootNode()); DI != E; ++DI) {
// Get the set to update for this block
ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
DenseMap<Value*, LoadInst*> lastSeenLoad;
BasicBlock* BB = DI->getBlock();
// A block inherits AVAIL_OUT from its dominator
if (DI->getIDom() != 0)
currAvail = availableOut[DI->getIDom()->getBlock()];
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE; ) {
changed_function |= processInstruction(BI, currAvail,
lastSeenLoad, toErase);
NumGVNInstr += toErase.size();
// Avoid iterator invalidation
++BI;
for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
E = toErase.end(); I != E; ++I) {
(*I)->eraseFromParent();
}
toErase.clear();
}
}
return changed_function;
}
Reference in New Issue View Git Blame Copy Permalink